U.S. patent application number 13/945781 was filed with the patent office on 2014-01-23 for multibeam transmitting and receiving antenna with multiple feeds per beam, system of antennas and satellite telecommunication system containing such an antenna.
The applicant listed for this patent is THALES. Invention is credited to Pierre BOSSHARD, Bernard CHARRAT, Philippe LEPELTIER, Judicael PRESSENSE.
Application Number | 20140022138 13/945781 |
Document ID | / |
Family ID | 47424923 |
Filed Date | 2014-01-23 |
United States Patent
Application |
20140022138 |
Kind Code |
A1 |
BOSSHARD; Pierre ; et
al. |
January 23, 2014 |
Multibeam Transmitting and Receiving Antenna with Multiple Feeds
Per Beam, System of Antennas and Satellite Telecommunication System
Containing Such an Antenna
Abstract
The transmitting and receiving antenna comprises an array of
feeds clustered by groups of four adjacent feeds along two
directions X, Y of a plane, each feed comprising two transmitting
ports and two receiving ports with orthogonal polarizations. For
each group of four adjacent feeds, the first, or the second,
transmitting ports, respectively the first, or the second,
receiving ports, corresponding to a same pair of frequency and
polarization values are connected two-by-two in the direction X
then two-by-two in the direction Y, the four interconnected
transmitting ports forming a transmitting beam and the four
interconnected receiving ports forming a receiving beam.
Inventors: |
BOSSHARD; Pierre;
(Tournefeuille, FR) ; LEPELTIER; Philippe;
(Castanet Tolosan, FR) ; PRESSENSE; Judicael;
(Toulouse, FR) ; CHARRAT; Bernard; (Toulouse,
FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
THALES |
Neuilly-sur-Seine |
|
FR |
|
|
Family ID: |
47424923 |
Appl. No.: |
13/945781 |
Filed: |
July 18, 2013 |
Current U.S.
Class: |
343/836 ;
343/835 |
Current CPC
Class: |
H01Q 19/136 20130101;
H01Q 25/007 20130101; H04B 7/18515 20130101; H01Q 13/0258 20130101;
H01Q 21/29 20130101; H01Q 1/288 20130101; H01Q 19/17 20130101; H01Q
21/064 20130101 |
Class at
Publication: |
343/836 ;
343/835 |
International
Class: |
H01Q 21/29 20060101
H01Q021/29; H01Q 21/06 20060101 H01Q021/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 20, 2012 |
FR |
12 02061 |
Claims
1. A multibeam transmitting and receiving antenna with multiple
feeds per beam comprising at least one reflector and one array of
several feeds illuminating the reflector, the feeds being clustered
into several groups offset with respect to each other in two
directions X, Y of a plane, each feed comprising a radiating
element connected to a radiofrequency channel, wherein: each feed
comprises a first and a second transmitting port having a same
transmission frequency and orthogonal polarizations to each other
and a first and second receiving port having a same reception
frequency and orthogonal polarizations to each other, the reception
frequency being different from the transmission frequency, the
feeds are clustered by groups of four adjacent feeds in the
directions X and Y, for each group of four adjacent feeds, the
first or the second transmitting ports, and the first or the second
receiving ports, corresponding to a same frequency and to a same
polarization are connected two-by-two in the direction X then
two-by-two in the direction Y, the four interconnected transmitting
ports forming a transmitting beam and the four interconnected
receiving ports forming a receiving beam.
2. The antenna of claim 1, wherein two consecutive adjacent groups
in the direction X are spaced by a first pitch L1 corresponding to
a feed in the direction X and share two feeds in common, and
wherein two consecutive adjacent groups in the direction Y are
spaced by a second pitch L2 corresponding to two feeds in the
direction Y and do not share any feed in common, each group of four
feeds forming a transmitting beam and a receiving beam.
3. The antenna of claim 1, wherein two consecutive adjacent groups
in the direction X are spaced by a first pitch L1 corresponding to
a feed in the direction X and two consecutive adjacent groups in
the direction Y are spaced by a second pitch L2 corresponding to a
feed in the direction Y, each group of four feeds forming a
transmitting beam and a receiving beam.
4. The antenna according to claim 1, wherein for the forming of
each beam, the connections between the transmitting or receiving
ports of a group of four feeds are made by distribution circuits,
the distribution circuits dedicated to the forming of different
beams being independent from each other.
5. The antenna of claim 2, wherein for the first of the two groups
of feeds, the first transmitting ports, respectively the first
receiving ports having the same polarization, are connected
two-by-two in the direction X then two-by-two in the direction Y
and wherein for the second of the two groups of feeds, the second
transmitting ports, respectively the second receiving ports having
the same polarization, are connected two-by-two in the direction X
then two-by-two in the direction Y.
6. A system of transmitting and receiving antennas with formation
of contiguous beams, comprising two transmitting and receiving
antennas according to claim 1, the two transmitting and receiving
antennas having identical directions of alignment in a first
direction U in space and angularly offset in a second direction V
in space.
7. The system of transmitting and receiving antennas with formation
of contiguous beams of claim 6, wherein the angular offset between
the directions of alignment of the two transmitting and receiving
antennas corresponds to an offset, equal to one spot, of the lines
of spots formed on the ground by the two antennas.
8. A satellite telecommunication system comprising at least one
system of two transmitting and receiving antennas according to
claim 6.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to foreign French patent
application No. FR 1202061, filed on Jul. 20, 2012, the disclosure
of which is incorporated by reference in its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to a multi-beam transmitting
and receiving antenna with Multiple Feeds Per Beam, a system of
transmitting and receiving antennas with formation of contiguous
beams and a satellite telecommunication system comprising one such
antenna system. It notably applies to the domain of satellite
telecommunications and in particular to the optimization of
satellite resources by frequency re-use in a so-called four-colour
scheme.
[0003] The multibeam antennas under consideration are composed of
at least one reflector, for example an asymmetric paraboloid with a
feed offset with respect to the radiated beams known as an "offset
paraboloid", and an array of primary feeds placed at the focus of
the reflector. Each primary feed is composed of a radiating
element, for example of horn type or any other known type, and a
radiofrequency RF channel feeding the radiating element.
BACKGROUND
[0004] Conventionally, to each feed of the focal array there
corresponds a narrow beam radiated by the antenna and an area of
ground coverage known as a "spot". It is possible to obtain a
radiation of the antenna by multiple beams if the elementary beams
are decoupled from each other, the decoupling being either spatial
or obtained by the use of orthogonal polarizations or different
frequencies between two adjacent beams. The laws of geometry make
it possible to project the desired ground coverages into the focal
plane of the antenna and to correctly position the phase centre of
each primary feed corresponding to each spot. When the coverage is
composed of spots regularly arranged on the ground, the offset
between two adjacent spots directly determines the space separating
two adjacent feeds in the focal plane.
[0005] The formation of a large number of contiguous narrow beams
implies the fabrication of an antenna comprising a large number of
elementary radiating elements, placed in the focal plane of a
parabolic reflector. In the case of a conventional antenna in SFPB
(Single Feed Per Beam) configuration corresponding to one feed per
beam, the volume allocated for the placing of a radiofrequency RF
channel intended to perform the transmitting and receiving
functions in circular bipolarization is bounded by the radiative
surface of a radiating element.
[0006] In this configuration where each feed, composed of a
radiating element coupled with a radiofrequency channel, forms a
beam, each beam formed is transmitted, for example by a dedicated
horn constituting the elementary radiating element, and the
radiofrequency channel carries out, for each beam, the
transmitting/receiving functions in single polarization in a band
of frequencies chosen according to the needs of the users. To
obtain good radiation efficiency for the spots, the horns of the
radiating arrays must enjoy enough space to enable them to be
sufficiently directive, in order to illuminate the edge of the
reflectors at sufficiently low levels and thus make it possible to
limit losses due to spillover. Since the spots are interleaved, the
space between two feeds of an antenna may not be compatible with
the physical dimensions of the horns to attain the desired
radiofrequency performance. For example, this is the case for spot
sizes of less than 1.degree.. To solve this problem, three or four
different antennas, each producing a third or respectively a
quarter of the coverage, are generally chosen. Thus, two adjacent
spots of the coverage are not produced by the same antennas. When
there is no constraint on the layout of the antenna array, this
configuration generally makes it possible to obtain very effective
antenna performance. However, when the diameter of the beams
diminishes, the geometrical constraints increase and it is not
possible to have sufficient space to install each horn despite
sharing the coverage over three or four antennas. For very narrow
spots of a size between 0.2.degree. and 0.4.degree., the space
allocated to each feed of the focal array becomes very small and
the reflector is seen by each feed of the focal array under a
sub-tended angle not allowing the feeds to produce sufficient
directivity to avoid spillover losses.
[0007] A second antenna configuration allowing the forming of a
large number of contiguous narrow beams uses a system of two
antennas in MFPB (Multiple Feeds Per Beam) configuration using
several feeds per beam. Generally, the first antenna Tx operates as
the transmitter, the second antenna Rx operates as the receiver,
and for each antenna, each beam is formed by combining the signals
issued by several adjacent elementary feeds, some of these feeds
being re-used to form contiguous beams. A satisfactory radiation
efficiency is obtained thanks to the re-use of the feeds, which
participate in the formation of several beams, making it possible
to increase the radiative surface allocated to each beam and to
reduce spillover losses. When the feeds are shared between several
beams of the same frequency and polarization, it is possible to
create a condition of independence between the beams sharing
radiating elements by imposing the formation of so-called
orthogonal laws. Orthogonality is achieved by using directional
couplers which isolate two-by-two the distribution circuits of the
beamforming network BFN which share the same radiating elements.
However, the orthogonality constraints provoke a deformation of the
radiation patterns of the antennas and an increase in the ohmic
losses of the recombining circuits related to the complexity of the
distribution circuits. The cumulative losses are often significant,
i.e. of the order of 1 dB. Furthermore, it is necessary to limit
the complexity of the beamformers to a re-use rate of two radiating
elements per spot. This leads to the physical separation of the
combining circuits of two adjacent beams by a distance
corresponding to two adjacent radiating elements. For spots with an
angular offset of between 0.2.degree. and 0.3.degree., the apparent
focal length can be very large, for example of the order of 10
metres. Finally, the re-use of the feeds when forming two adjacent
beams presents major drawbacks related to the dimensions of the
combining circuits, the weight of the beamformer and the complexity
of forming the amplitude and phase laws for each antenna. Indeed,
for a re-use of two feeds per polarization, the number of
elementary radiofrequency RF channels increases by a factor of
greater than four with the number of spots to be formed. Thus, for
100 spots, a number of RF channels greater than 400 radiating
elements is required, which necessitates a surface in the focal
plane of the order of 500 mm*500 mm. The weight and the volume of
the beamformer then become unmanageable.
[0008] It is known from patent FR 2 939 971 that a very compact
radiofrequency channel can be made using an asymmetric OMT with two
branches, associated with an unbalanced branched coupler. This
radiofrequency channel operates in dual polarization as transmitter
and receiver and comprises radiofrequency components and combining
circuits, the dimensions of which do not exceed the horn
diameter.
SUMMARY OF THE INVENTION
[0009] The aim of the invention is to create a multibeam
transmitting and receiving antenna with multiple feeds per beam and
a system of transmitting and receiving antennas with formation of
contiguous beams not involving the drawbacks of existing antenna
systems, making it possible to dispense with the use of orthogonal
BFNs for the forming of adjacent beams and making it possible to
obtain a large number of narrow contiguous beams having an angular
aperture of between 0.2.degree. and 0.4.degree., with good covering
of the ground coverage areas, called spots, corresponding to each
beam, while at the same time reducing the number and dimensions of
the antennas.
[0010] To this end, the invention relates to a multibeam
transmitting and receiving antenna with multiple feeds per beam
comprising at least one reflector and an array of several feeds
illuminating the reflector, the feeds being clustered into several
groups offset with respect to each other along two directions X, Y
of a plane, each feed comprising a radiating element connected to a
radiofrequency channel. Each feed comprises a first and second
transmitting port having a same transmission frequency and
orthogonal polarizations to each other, and a first and second
receiving port having a same reception frequency and orthogonal
polarizations to each other, the reception frequency being
different from the transmission frequency. The feeds are clustered
into groups of four adjacent feeds in the directions X and Y. For
each group of four adjacent feeds, the first or the second
transmitting ports, and the first or the second receiving ports,
corresponding to a same frequency and to a same polarization, are
connected two-by-two in the direction X then two-by-two in the
direction Y, the four interconnected transmitting ports forming a
transmitting beam and the four interconnected receiving ports
forming a receiving beam.
[0011] Advantageously, two consecutive adjacent groups in the
direction X can be spaced by a first pitch L1 corresponding to a
feed in the direction X and share two feeds in common, two
consecutive adjacent groups in the direction Y can be spaced by a
second pitch L2 corresponding to two feeds in the direction Y and
not share any feed in common, each group of four feeds forming a
transmitting beam and a receiving beam.
[0012] Alternatively two consecutive adjacent groups in the
direction X can be spaced by a first pitch L1 corresponding to a
feed in the direction X and two consecutive adjacent groups in the
direction Y can be spaced by a second pitch L2 corresponding to a
feed in the direction Y, each group of four feeds forming a
transmitting beam and a receiving beam.
[0013] Advantageously, for the formation of each beam, the
connections between the transmitting or receiving ports of a group
of four feeds are achieved by distribution circuits, the
distribution circuits dedicated to the formation of different beams
being independent from each other.
[0014] Advantageously, for the first of the two groups of feeds,
the first transmitting ports, respectively the first receiving
ports having the same polarization, are connected two-by-two in the
direction X then two-by-two in the direction Y and for the second
of the two groups, the second transmitting ports, respectively the
second receiving ports having the same polarization, are connected
two-by-two in the direction X then two-by-two in the direction
Y.
[0015] The invention also concerns a system of transmitting and
receiving antennas with formation of contiguous beams comprising
two transmitting and receiving antennas, the two transmitting and
receiving antennas having identical directions of alignment in a
first direction U in space and angularly offset in a second
direction V in space.
[0016] Advantageously, the angular offset between the directions of
alignment of the two transmitting and receiving antennas
corresponds to an offset, equal to one spot, of the lines of spots
formed on the ground by the two antennas.
[0017] The invention also relates to a satellite telecommunication
system comprising at least one system of two transmitting and
receiving antennas.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Other peculiarities and advantages of the invention will
appear clearly following the description given by way of purely
illustrative and non-limiting example, referring to the
diagrammatic drawings appended which show:
[0019] FIG. 1a: a diagram of an example transmitting and receiving
feed, according to the invention;
[0020] FIG. 1b: a cross-sectional diagram illustrating the four
ports of the transmitting and receiving feed of FIG. 1a, according
to the invention;
[0021] FIG. 1c: a diagram of an example radiofrequency channel
functioning in dual polarization during transmission and reception,
according to the invention;
[0022] FIG. 2a: a diagram of an example illustrating a system of
two transmitting and receiving antennas with formation of
contiguous beams, according to the invention;
[0023] FIG. 2b: a diagram illustrating an example of ground
coverage produced by the system of two transmitting and receiving
antennas with formation of contiguous beams, according to the
invention;
[0024] FIG. 3: a diagram of a first example of a configuration of
the groups of four feeds of each transmitting and receiving antenna
with a sharing of two feeds between two adjacent groups in a
direction X of the array of feeds, no sharing of feeds along the
direction Y, in the case of an arrangement of the feeds in a
hexagonal mesh array and in the case where the directions X and Y
make an angle different from 90.degree. with each other, the feeds
not being shown here to simplify the diagram, according to the
invention;
[0025] FIG. 4: a diagram illustrating a first level of distribution
connecting two-by-two, in the direction X, the ports of the feeds
of a transmitting and receiving antenna, according to the
invention;
[0026] FIG. 5: a diagram illustrating a second level of
distribution connecting two-by-two, in the direction Y, the ports
of the feeds of a transmitting and receiving antenna, according to
the invention.
[0027] FIG. 6a: a diagram of a second example of a configuration of
the groups of four feeds of each transmitting and receiving antenna
with sharing of a single feed between two adjacent groups in the
direction X and between two adjacent groups in the direction Y, in
the case of an arrangement of the feeds in a hexagonal mesh and in
the case where the directions X and Y make an angle of 90.degree.
with each other, according to the invention;
[0028] FIG. 6b: an example of coverage obtained with two antennas
having the configuration of FIG. 6a, according to the
invention;
[0029] FIG. 7a: a diagram of a third example of a configuration of
the groups of four feeds of each transmitting and receiving antenna
with sharing of a single feed between two adjacent groups in the
direction X and between two adjacent groups in the direction Y, in
the case of an arrangement of the feeds in a square mesh, the two
directions X and Y making an angle of 90.degree. with each other,
according to the invention,
[0030] FIG. 7b: a diagram of a particular case of an antenna
corresponding to FIG. 7a, according to the invention.
[0031] FIG. 7c: an example of coverage obtained with a single
antenna having the configuration corresponding to the particular
case of FIG. 7b, according to the invention.
DETAILED DESCRIPTION
[0032] FIG. 1a shows an example of a transmitting and receiving
feed according to the invention. The transmitting and receiving
feed 10 is composed of a radiating element 11, for example of horn
type, and of a radiofrequency channel 12 connected to the horn 11.
The radiofrequency channel 12 shown in cross-section in FIG. 1c is
a new-generation channel with reduced dimensions which operates in
dual polarization for transmission and reception. For transmission,
the radiofrequency channel 12 comprises two transmitting ports T1,
T2 and for reception, the radiofrequency channel comprises two
receiving ports R1, R2, the four ports T1, T2, R1, R2 shown in
cross-section in FIG. 1b being connected to the radiating element
11 by way of radiofrequency components and combining circuits 13.
The feed 10 is represented in the diagram by a circle surrounding
the four ports in FIG. 1b. The radiofrequency components include a
compact exciter 14, for example an orthomode transducer (OMT), with
circular or square cross-section, coupled to a branched coupler 15
by way of two coupling slots 16, 17, spaced by an angle of
90.degree., arranged in the longitudinal wall, or walls, of the
exciter 14. The two transmitting ports T1, T2 are connected to two
different branches of the branched coupler 15. The exciter 14
extends longitudinally along an axis Z between two opposite ends
18, 19 situated along the longitudinal axis Z. The radiating
element 11, for example of the horn type, is connected to a first
end 18 of the exciter 14 and the two receiving ports R1, R2 are
connected to a second end 19 of the exciter 14. The OMT feeds the
horn 11 (during transmission), or is fed by the horn 11 (during
reception), selectively either with a first electromagnetic mode
exhibiting a first polarization, or with a second electromagnetic
mode exhibiting a second polarization orthogonal to the first. The
first and second polarizations, with which are associated two
electric field components, are linear and known as horizontal
polarization and vertical polarization respectively.
[0033] The two transmitting ports T1, T2, in the same way as the
two receiving ports R1, R2, operate in two polarizations orthogonal
to each other, for example, right- and left-circular polarizations
or two linear polarizations orthogonal to each other. By using an
asymmetric OMT with two branches, associated with an unbalanced
branched coupler 15, as described in the document FR 2 939 971, the
feed 10 is very compact and the dimensions of the radiofrequency
components and of the combining circuits of the radiofrequency
channel 12 do not exceed the diameter of the horn 11, i.e. around
30 mm. For an antenna comprising an array of identical horns
arranged regularly, each radiofrequency channel dedicated to each
horn enters into a hexagonal mesh of dimensions of approximately 30
mm corresponding to the horn diameter.
[0034] FIG. 2a illustrates a system of transmitting and receiving
antennas with formation of contiguous beams, according to the
invention. The system of antennas comprises two antennas 21, 22,
each antenna operating as transmitter Tx and as receiver Rx, the
transmission frequencies F1 being different from the reception
frequencies F2. The two antennas 21, 22 each comprise a radiating
array 23, 24, each radiating array 23, 24 comprising several feeds
organized in two directions X and Y of a plane. Each feed comprises
a radiating element 11 connected to a radiofrequency channel 12,
two transmitting ports T1, T2 and two receiving ports R1, R2, the
two transmitting ports T1, T2 having polarizations P1, P2
orthogonal to each other and the two receiving ports R1, R2 having
polarizations P1, P2 orthogonal to each other. The polarizations of
the transmitting ports T1, T2 and of the receiving ports R1, R2 can
for example be linear or circular. Different optical configurations
of the antenna are possible, for example Gregorian, Cassegrain or
others, and the antenna can notably contain one or two reflectors
associated with the radiating array. In FIG. 2a, each antenna 21,
22 comprises a respective parabolic reflector 25, 26 illuminated by
the radiating array 23, 24 placed in the focal plane of the
parabolic reflector of the corresponding antenna 21, 22. Each
antenna is aligned in a respective direction of alignment 27, 28
towards a chosen area of ground coverage, for example a region, a
country, a group of several countries, a continent, or another
territory.
[0035] When the territory to be covered is of elongate form and
extends essentially in a single direction U in space, such as Chili
for example, the invention advantageously makes it possible to
cover with a single transmitting and receiving antenna the entire
territory during transmission and reception with good overlap of
the spots achieved on the ground.
[0036] When the territory to be covered extends in two directions
U, V of the Earth's surface, in certain configurations of the
antenna feeds, notably when the feeds are arranged in a square
mesh, it is possible to obtain a quasi-complete coverage with a
single antenna according to the invention. In other configurations,
notably when the feeds are arranged in a hexagonal mesh, it can be
necessary to have recourse to two transmitting and receiving
antennas of the same dimensions to obtain good overlap of the spots
in both directions U and V during transmission and reception. In
the case where two antennas are used to produce complete coverage,
the first antenna 21 is intended to provide the totality of the
desired coverage, during transmission and reception, in a first
direction U in space and a first half of the desired coverage in a
second direction V in space. The second antenna 22 is intended to
fill in the coverage holes of the first antenna 21, during
transmission and reception, in the second direction V in space to
guarantee a second half of the desired coverage. The two antennas
then make it possible to reconstitute the whole of the desired
coverage in the directions U and V.
[0037] By way of non-limiting example, FIG. 2b illustrates an
example of coverage produced by the two antennas 21, 22. The spots
1 correspond to ground coverage areas produced by the first antenna
21 and the spots 2 correspond to ground coverage areas produced by
the second antenna 22. This figure shows that in the direction U,
the spots 1 produced by the first antenna 21 are touching with a
slight overlap between two adjacent spots 1 whereas in the
direction V, the spots 1 do not touch and exhibit coverage holes.
The spots 2 produced by the second antenna 22 constitute additional
lines of spots 2, each line of spots 2 being interleaved between
two consecutive lines of spots 1, thus making it possible to fill
the coverage holes of the first antenna 21. By way of non-limiting
example, with two antennas each comprising 64 radiating elements
arranged in a matrix of 8 lines and 8 columns, the 128 radiating
elements of the two antennas make it possible to form 42 contiguous
spots on the ground in two directions in space, with good overlap
of the spots in both directions in space.
[0038] For each antenna 21, 22, each transmitting beam and each
receiving beam, corresponding to a spot on the ground, is formed by
combining the signals issuing from four adjacent radiofrequency
feeds arranged in a 2*2 matrix. Two adjacent beams are formed by
two adjacent groups in a first direction X or in a second direction
Y of the feed array.
[0039] FIG. 3 illustrates a first example of four-by-four grouping
of the radiofrequency feeds 10 in the case where the feeds are
distributed in an array as a hexagonal mesh, the same configuration
being also realizable with another type of mesh such as a square
mesh for example. In this example, the directions X and Y are not
chosen to be perpendicular to each other and can for example make
an angle of 120.degree. or 60.degree.. Each group of four feeds
makes it possible to form a transmitting beam and a receiving beam.
The beamforming device does not contain any coupler but only
distribution circuits made of waveguides connecting ports of the
same colour to each other. Each beam is formed by dedicated
distribution circuits, independent from one beam to another. The
distribution circuits operate during transmission as signal
combiners and during reception as signal splitters. The
distribution circuits dedicated to the formation of a transmitting
beam, connect one of the transmitting ports T1 or T2 of the four
feeds of a same four-by-four group, the four interconnected
transmitting ports having a same colour. Similarly, the
distribution circuits dedicated to the formation of a receiving
beam, connect one of the receiving ports R1 or R2 of the four feeds
of a same four-by-four group, the four interconnected receiving
ports having a same colour. During transmission and reception, two
adjacent beams are formed by two groups G1, G2 adjacent in the
direction X or G1, G3 adjacent in the direction Y, each group G1,
G2, G3, G4 . . . GN being each composed of four feeds 10, the two
adjacent groups G1, G2 being offset by a first pitch L1
corresponding to the dimensions of a feed in the first direction X
of the antenna, equal to the diameter D of a radiofrequency feed 10
in FIG. 3, and the two adjacent groups G1, G3 being offset by a
second pitch L2 corresponding to the dimensions of two feeds in the
second direction Y of the antenna, equal to the diameter 2D of two
radiofrequency feeds in FIG. 3. Thus, in this first example, in the
direction X, the two groups G1, G2 of four radiofrequency feeds
which participate in the formation of two adjacent beams share two
feeds in common whereas in the direction Y, the two groups G1, G3
of four radiofrequency feeds which participate in the formation of
two adjacent beams do not have any feed in common. The sharing of
the radiofrequency feeds between two adjacent groups is therefore
only realized in a single direction X of the antenna, which makes
it possible to guarantee, with a single antenna operating as
transmitter and receiver, a coverage that is complete in the first
direction U in space but incomplete in the second direction V in
space. The second antenna 22 makes it possible to form, during
transmission and reception, additional lines of spots 2 offset in
the second direction V in space and to fill the coverage holes of
the first antenna 21, during transmission and reception.
[0040] The beams formed by each antenna are formed by a beamformer
comprising two levels of distribution connecting, for each group of
four feeds, the ports of a same colour, i.e. the same frequency and
the same polarization. Thus, in accordance with the invention, each
beam is advantageously formed by dedicated distribution circuits
that are independent of the distribution circuits forming the other
beams. Each beam is formed by a group of four feeds by connecting,
via dedicated distribution circuits, four ports of the four feeds
to each other, the four connected ports having a same colour, each
colour corresponding to a frequency and polarization pair (F1, P1),
(F2, P2), (F2, P1), (F2, P2). Each group of four feeds thus
comprises four transmitting ports of a same colour connected to
each other and making it possible to form a transmitting beam and
four receiving ports of a same colour connected to each other and
making it possible to form a receiving beam. Each feed of a same
group comprising two transmitting ports and two receiving ports, a
transmitting port and a receiving port remain available for the
forming of two other beams, respectively for transmitting and
receiving, with feeds of an adjacent group.
[0041] An example of a first level of distribution is shown in FIG.
4. In this example, the first distribution level comprises, for
each group of four radiofrequency feeds, two first distribution
circuits C1, C2 connecting two-by-two the first transmitting ports
T1a and T1b and receiving ports R1a, R1b of the two radiofrequency
feeds 10a, 10b adjacent in the direction X, and two first
distribution circuits C3, C4 connecting two-by-two the first
transmitting ports T1c and T1d and receiving ports R1c, R1d of the
two radiofrequency feeds 10c, 10d adjacent in the direction X,
hence four first distribution circuits C1 to C4 per group of four
radiofrequency feeds 10a, 10b, 10c and 10d. The first distribution
circuits C1, C2 connect, two by two and in the direction X, two
first transmitting ports T1a, T1b, respectively two first receiving
ports R1a, R1b, of the two first and second adjacent feeds 10a, 10b
of a same group G1 of four feeds. The two first transmitting ports
T1a, T1b connected have the same polarization P1 and the same
operating frequency F1, the two first receiving ports R1a, R1b
connected have the same polarization P1 and the same operating
frequency F2. Similarly, the first distribution circuits C3, C4
connect, two-by-two and in the direction X, two first transmitting
ports T1c, T1d, respectively two first receiving ports R1, Rid, of
two third and fourth adjacent feeds 10c, 10d of the same group G1
of four feeds. The two first transmitting ports T1c, T1d connected
have the same polarization P1 and the same operating frequency F1,
the two first receiving ports R1c, R1d connected have the same
polarization P1 and the same operating frequency F2.
[0042] Each radiofrequency feed 10a comprising four ports of which
two transmitting ports T1a, T2a and two receiving ports R1a, R2a,
after the combining carried out between the first transmitting
ports T1a, T1b, respectively receiving ports R1a, R1b, connected to
two adjacent radiofrequency feeds 10a, 10b of the first group G1 of
four feeds, the two radiofrequency feeds 10a, 10b each comprise a
second transmitting port T2a, T2b and a second receiving port R2a,
R2b which are free and which can in turn be respectively connected,
in the direction X, to a second transmitting port and to a second
receiving port of an adjacent feed belonging to a second group G2
of four feeds, offset from the first group G1 by a pitch L1
corresponding to one feed. For example, in FIG. 4, the four feeds
of a second group G2 are the feeds 10b, 10'a, 10d, 10'c. The
transmitting T2b and receiving R2b ports of the feed 10b are
respectively connected to the transmitting ports T'2a and R'2a of
the feed 10'a and the ports T2d and R2d of the feed 10d are
respectively connected to the ports T'2c and R'2c of the feed 10'c.
The connections between two respective ports of two adjacent feeds
are realized in the same way for all the groups of four feeds up to
the edges of the radiating array. The feeds situated on the edges
of the radiating array of the antenna have only one adjacent feed
and each comprise each one transmitting port T2a, T2c and one
receiving port R2a, R2c which remain free.
[0043] An example of a second level of distribution is shown in
FIG. 5. The second distribution level comprises second distribution
circuits D1, D2 which respectively connect, two-by-two and in the
direction Y, for each group G1 of four radiofrequency feeds 10a,
10b, 10c, 10d, on the one hand, the two first transmitting ports
T1a, T1b of the first and second feeds 10a, 10b connected in the
direction X to the two first transmitting ports T1c, T1d of the
third and fourth radiofrequency feeds connected in the direction X
and on the other hand, the two first receiving ports R1a, R1b of
the first and second radiofrequency feeds 10a, 10b connected in the
direction X to the two first receiving ports R1c, R1d of the third
and fourth radiofrequency feeds 10c, 10d connected in the direction
X. The output of the distribution circuit D1 is a transmitting port
Tx of a spot of frequency F1 and polarization P1 and the output of
the distribution circuit D2 is a receiving port Rx of a spot of
frequency F2 and of polarization P1. Similarly, for each group of
four feeds, all the ports of the same frequency and of the same
polarization connected two-by-two by the first distribution
circuits of the first level of distribution are connected to each
other by a distribution circuit of the second level in such a way
as to form all the transmitting and receiving spots of the antenna.
During transmission the distribution circuits operate as signal
combiners, during reception, the operation of the beamformer of the
antenna is inverted and the distribution circuits operate as signal
splitters.
[0044] In the direction U, each spot is produced by a group of four
radiofrequency feeds and two adjacent spots are produced by two
adjacent groups offset by a single feed and which therefore share
two feeds in common. This configuration makes it possible, with a
single antenna and without using orthogonal circuits for the
forming of two adjacent beams, to obtain good spot overlap in the
direction U and a ground coverage area, during transmission and
reception, that does not exhibit holes in this direction U. In the
V direction, each spot produced by a group of four radiofrequency
feeds and two adjacent spots are produced by two adjacent groups
offset by two feeds and which therefore do not share any feed. The
spots obtained with a single antenna do not overlap in the
direction V and the ground coverage area exhibits holes in this
direction V. This type of ground coverage can however be enough to
cover territories of elongated form such as Chili for example. In
this case a single transmitting and receiving antenna 21 can be
adequate.
[0045] Regarding larger territories extending along two directions
U and V in space, two transmitting and receiving antennas 21, 22
can be necessary to obtain complete coverage, as shown in FIGS. 2a
and 2b. So that the second antenna 22 fills the holes in the
coverage, in the direction V, of the first antenna 21, the
alignment direction 28 of the second antenna 22 is offset angularly
with regard to the direction of alignment 27 of the first antenna
21. The angular offset of the direction of alignment of the two
antennas, the one with respect to the other, corresponds to an
offset, in the direction V, of the lines of spots 2 formed on the
ground by the second antenna 22 in relation to the lines of spots 1
formed by the first antenna 21, the directions of alignment 27, 28
of the two antennas being identical in the direction U. Each
antenna forms the totality of the spots during transmission and
reception in the direction U and one line of spots out of two in
the direction V. The offset of the lines of spots formed by the
second antenna 22 corresponds approximately to the diameter of one
spot, which makes it possible to insert, in the direction V, an
additional line of spots 1 between two successive lines of spots 1
formed by the first antenna 21, to thus obtain a good overlap
between the spots 1, 2 and to fill the holes in the coverage
produced by the two transmitting and receiving antennas.
[0046] FIG. 6a illustrates a second example of four-by-four
grouping of radiofrequency feeds 10 in the case where the feeds are
distributed in an array as a hexagonal mesh, the two directions X
and Y making an angle of 90.degree. with each other. In this second
example, two adjacent groups in the direction X share a single
radiofrequency feed and two adjacent groups in the direction Y also
share a single feed. The two adjacent groups G1, G2 are offset by a
first pitch L1 corresponding to the dimensions of a single feed in
the first direction X of the antenna and the two adjacent groups
G1, G3 are offset by a second pitch L2 corresponding to the
dimensions of a single feed in the second direction Y of the
antenna, the pitch L2 therefore being equal to the pitch L1. An
example of coverage obtained with the configuration of FIG. 6a is
shown in FIG. 6b. This coverage is obtained using two transmitting
and receiving antennas to produce complete coverage during
transmission and reception. The spots 1 of the first and of the
third horizontal line are produced with a first antenna, the spots
2 of the second horizontal line are produced with a second
antenna.
[0047] FIG. 7a illustrates a third example of four-by-four grouping
of radiofrequency feeds 10 in the case where the feeds are
distributed in an array as a square mesh, the two directions X and
Y making an angle of 90.degree. with each other. In this third
example, two adjacent groups share a single radiofrequency feed,
the sharing being realized between the adjacent groups in the
direction X and between the adjacent groups in the direction Y. As
in the case of FIG. 6a, the two adjacent groups G1, G2 are offset
by a first pitch L1 corresponding to the dimensions of a single
feed in the first direction X of the antenna, and the two adjacent
groups G1, G3 are offset by a second pitch L2 corresponding to the
dimensions of a single feed in the second direction Y of the
antenna. In the case of a square mesh, the radiating elements may
be arranged more closely together than in the case of a hexagonal
mesh, thus allowing, for an identical antenna size, an increase in
the number of feeds and therefore the number of spots on the
ground. A single antenna can then produce a complete coverage
during transmission and reception. FIGS. 7b and 7c illustrate an
example of an antenna comprising a square mesh array and 16 feeds
grouped into five groups of four feeds, each group sharing one feed
with an adjacent group. The five groups of feeds make it possible
to produce five spots during transmission and five spots during
reception as shown in FIG. 7c illustrating the corresponding
coverage.
[0048] Complete coverage can also been obtained with a single
antenna by using a radiating array with a hexagonal mesh of which
the adjacent groups of feeds share a single feed in the directions
X and Y but with degraded antenna performance.
[0049] Although the invention has been described in relation to
particular embodiments, it is quite clear that it is in no way
limited thereto and that it comprises all the technical equivalents
of the means described as well as their combinations if these fall
within the scope of the invention.
* * * * *